When loading automobiles, the parts thereof, etc., just finished painting on trucks or ships and transporting remote places such as overseas, etc., it has been a practice to coat the automobiles, the parts thereof, etc. with paints containing wax as the main component to give a thickness of 5 to 40 μm so as to prevent them from being damaged, frosted, discolored, etc., by various floating matters and colliding matters such as dirts, dusts and rainwater. However, this method suffers from some problems, for example, that uniform protection can be hardly achieved thereby due to difficulties in forming a wax coating film of a uniform thickness; that the paint film may be easily stained; that the paint film is liable to be damaged by acid rain; that the wax, etc. would ooze out onto the paint film and thus cause discoloration, etc.; that a large labor is required in forming the paint film; and that use of a solvent and the waste liquid treatment frequently cause environmental problems.
On the other hand, there are known various surface protecting sheets comprising a support and a pressure-sensitive adhesive layer formed thereon. JP-A-2-199184 and JP-A-6-73352 propose protecting sheets for painted adherends having films provided with radiation-cured pressure-sensitive adhesive layers with a lowered glass transition temperature or polyisobutyrene-based rubber pressure-sensitive adhesive layers (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). The above-mentioned problems can be solved by using this sheet-like system.
However, the conventional protecting sheets suffer from a problem that when these sheets are peeled off from paint films of automobiles, there arise hardly repairable damages (i.e., discoloration or denaturation) of the paint films. These damages remarkably arise in particular in curved surface portions of automobiles.
To overcome these problems, the present inventors have conducted extensive studies and, as a result, found that the above-mentioned damages occur based on the following mechanism. Namely, rainwater or washing liquor (for example, window washer) penetrates into a paint film through wrinkles formed in the step of adhering a protecting sheet to an adherend. Next, the liquid is pooled in edges of entrapped air and concentrated therein due to the evaporation of moisture, thus causing the damages such as discoloration or denaturation of the paint film of automobile. Thus, it can be understood why curved surface portions with frequent wrinkle formation would be seriously damaged. Accordingly, the present inventors have studied to establish an adhesion cover system freed from wrinkles. However, wrinkling is unavoidable in the conventional protecting sheets.